Y-tube to Dual

[mySAVIOReigns]

I've been thinking about this for a long time. Let me know what you guys think, if I should make any changes.
Right now, I have the stock Y-tube exhaust, cat, and a glass pack muffler.

I want to change it to dual exhaust, so I'm thinking of getting some shorty headers, heading out to the junkyard and getting an old dual exhaust pipe system off of a similar chevy, buying a CAT and another muffler, then having a muffler or weld shop weld it all together for me. Then hopefully, I can get this thing a little better gas mileage

Also, anyone know if there is a carb that will bolt on in place of my Rochester 4BBL? Preferrebly an Edelbrock or something. I hear that you have to replace the intake manifold, but if there are any options before doing that, I'd option for them first.

Thanks